When there is no value to your own life, there's not likely to be much value in anyone else's. When there are no consequences to your actions, any action is permissible. When there's nothing beyond the immediate and you, there's no reason to be morally responsible.
Now add in the brain-altering "medications" many young men are on and you're sitting on a powder keg playing with matches.
I believe that the Columbine killers were on medications.